1. Field of the Invention
This invention relates to power steering gears and more particularly to a steering limiter coupled to the input of a power steering gear to establish left and right turn limit stops to prevent engagement of the dirigible wheels with their stops and thereby avoid closing of the power steering gear valve and resulting operation of the power steering pump in relief.
2. Description of the Prior Art
Power steering systems generally incorporate engine driven hydraulic pumps which supply pressure fluid to the open center valves of the power steering gears. To increase pump service life, relief valving is provided in the pump to limit pump output pressure. However, if the flow of oil from the pump remains blocked for some time, as when the dirigible wheels of the vehicle are steered against their wheel stops, curbing or deep sand or mud, continued operation in pump relief may result in pump overload with higher fluid temperatures and reduced pump service life.
Prior to the present invention, some power steering gears incorporated internal relief valve constructions which were actuated as the steering approached wheel stop or internal stop of the gear to prevent full lock power steering and resulting operation of the pump in pressure relief. While such pump saver devices have provided benefits in the power steering field, particularly in working vehicles such as gravel pit trucks which frequently operate in a full lock power steering situation, they are relatively complex and expensive. The pump saver devices internal of the gear add to cost and complexity of the gear. with these devices, there is the possibility of reduction of steering assist due to inadequate sealing or seating of the unloading valve or external leakage past the seals on the threaded adjusters for such devices.